Multiple transmit and receive antennas have been proposed to provide both increased robustness and capacity in next generation Wireless Local Area Network (WLAN) systems. The increased robustness can be achieved through techniques that exploit the spatial diversity and additional gain introduced in a system with multiple antennas. The increased capacity can be achieved in multipath fading environments with bandwidth efficient Multiple Input Multiple Output (MIMO) techniques. A multiple antenna communication system increases the data rate in a given channel bandwidth by transmitting separate data streams on multiple transmit antennas.
In the current IEEE 802.11a/g standard, for example, each channel is 20 MHz wide and there are 64 possible subcarriers within each 20 MHz channel. Of the 64 possible subcarriers, however, only 48 tones are employed to carry data in the 802.11 standard. It is noted that twelve tones are not used at all, including one blank tone at DC (0 MHz), and four pilot tones are employed that do not carry any user information. Thus, only 75 percent of the available subcarriers are employed to carry user data.
A number of techniques have been proposed or suggested for further increasing the data throughput in multiple antenna communication systems. For example, a channel bonding technique has been proposed that increases the channel bandwidth to 40 MHz and the number of subcarriers to 128. When the 802.11a standard is extended in such a two-fold manner to provide a 40 MHz channel bandwidth, it would likewise be expected to double the number of subcarriers that are employed to carry user information from 48 to 96 subcarriers. A need exists, however, for an ever greater improvement in efficiency and throughput. A further need exists for methods and apparatus for increasing throughput in a multiple antenna communication system using additional subcarriers.